Pilot-wire supervisory circuits



May 4, 1943 M. A. BosrwlcK Erm. 2,318,364

PILOT-WIRE SUPERVISORY CIRCUIT Filed Sept. l0, 1940 Patented May 4, 1943 PILOT-HIRE SUPERVISOR-Y CIRCUITS Myron A. Bostwick, Budd Lake, and Roy M.

Smith, Livingston, N. J., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsyl- Vania Application September 10, 1940, Serial No. 356,136

10 Claims.

Our invention relates to supervisory circuits for pilot wires, and particularly for pilot-Wire systems which are utilized for the purpose of comparing the directions of current-HOW at the two ends of an alternating-current transmissionline section which is being protected against faults within the protected section. The supervisory pilot-Wire circuit has heretofore been utilized to circulate a small direct current which does not interfere with the operation of the transmission-line protective relays, the circulating direct current being utilized in the pilot wire for the purpose of supervising the pilot Wire so as to respond to short-circuits, open-circuits, or a grounded conductor in the pilot wire. Such supervised pilot-Wire systems are described and claimed in an application of M. A. Bostwick, Serial No. 278,845, filed June 13, 1939, patented March 10, 1942, Patent No. 2,276,150, and in a patent of E. L. Harder, No. 1,953,103, granted April 3, 19,34, both assigned to the Westinghouse Electric &Manufacturing Company.

The principal object of our present invention is to improve upon supervisory pilot-Wire circuits of the class described, by providing `an indication of an accidental reversal of the pilot-wire connections, which, if undetected, would result in a faulty line-protecting relaying-operation, resulting in an erroneous tripping of the circuitbreakers in the transmission line, or a failure to trip such circuit-breakers during line-fault conditions. Such accidental reversal of the pilotwire connections is particularly apt to be encountered on leased telephone circuits which are used for pilot-Wire relaying, as the telephone companys service-men are not ordinarily aware of the importance of maintaining the correct pilot-wire polarity.

Other objects of our invention are to provide certain improvements in the operation of the supervisory pilot-wire circuits, particularly when said circuits are utilized for'the transmission of intellgence-communicating signals or currentchanges over the pilot Wire for any auxiliary purposes other than pilot-fault supervision, as will be subsequently described.

With the foregoing and other objects in View, our invention consists in the apparatus, combinations, circuits, systems and methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein:

rFigure 1 is a diagrammatic view of circuits and'apparatus utilizing a polarized direct-current relay at the receiving end of la supervised pilotwire system, for'the purpose of detecting acci- Cil dental reversal of the pilot-wire connections; and

Fig. 2 is a similar view of a supervised pilotwire system utilizing a rectifier at the receiving end 0f the supervisory circuit for the purpose of detecting accidental reversal of the pilot-Wire connections and also 'for the purpose of providing an Vautomatic reduction in 'the direct-current resistance of the supervisory circuit when overcurrent intelligence-comrnunicating signals are being transmitted over the pilot wire.

Our invention is illustrated, in both figures of Ithe drawing, as being utilized in connection with a three-phase transmission-line section 3 which is provided with current-comparing pilot-wire relay-protection. The particular system which is illustrated utilizes a, line-fault-responsive phasesequence relaying-apparatus HCB, at each end of the protected line-section 3, said apparatus including relay-contacts lIl for energizing the tripcircuit of a circuit-breaker 5 at that end of the protected line-section. The phase-sequence relaying-apparatus HCB rmay be cf any suitable type for deriving a single-phase electrical quantity, either a voltage or current, which is responsive to the polyphase line-currents as supplied by line-current transformers 6, a suitable relaying-apparatus for this purpose being shown in the Harder Patent No. 2,183,646, granted December 19, 1939, vand assigned to the Westinghouse Electric & Manufacturing Company.

The line-protecting relays HCB, besides being coupled to the line-current transformers 6, are also coupled to the respective primary windings I of tWo insulating transformers 8 having split secondary windings 9 and lil. The outer terminals of the split secondary windings 9 and I'Ii at the respective ends of the protected line-section are joined by a two-conductor pilot wire I2 to which our present invention is particularly directed, and the line-frequency currents are circulated in the pilot wire I2 through circuit-completing capacitors I3 and I4 which are utilized to join the inner ends of the respective spiit secondary windings 9 and ID at the two ends of the pilot Wire, respectively. The pilot wire I2 serves as a means for circulating and totalizing or comparing the line-frequency currents derived from 'the phase-sequence line-current-responsive apparatus HCB at the two ends of the protected line-section, so that the HCB relay-contacts 4 vserve as means for protecting the line-section against faults therein.

The pilot wire I2 is supervised by means of a circulating direct current which is connected to the pilot rire across the terminals of the capacitor I3 at one end of the pilot wire. The supervisory direct current is supplied from any suitable source such' as a transformer I6 and a rectier Il, the direct-current output-circuit of which is connected to the terminals of the capacitor I3 through the windings of a sensitive polarized relay I8 which has a front-contact I9 and a back-contact 20. The relay I8 is so chosen that, during normal pilot-wire conditions, the circulating supervisory direct current is of suiiicient magnitude to keep th'e back-contact 29 open, without closing the front-contact I9, so that the relay will respond, either to an overcurrent produced by a short-circuit or a groundfault on the pilot wire I2 or to an undercurrent caused by an open-circuiting or breakage of the pilot-wire circuit, in either event closing an alarm-circuit as indicated.

At the receiving end of the pilot wire I2, the capacitor I4 is shunted by a direct-current supervisory circuit, comprising a resistor 22 and an operating coil 23 of an undercurrent relay 2li, having a back-contact E which' energizes an alarm-circuit in response to an abnormal reduction in the circulated supervisory direct current such as will occur whenever the pilot wire I2 was either short-circuited, open-circuited or grounded.

In accordance with our invention, means are, or may be, provided at the receiving end of the pilot wire, that is, across the terminals of the capacitor I4, for securing a selective action, with respect to the circulating direct current, according to the direction of said circulating direct current at said receiving end. In the particular form of embodiment of our invention which is shown in Fig. l, this reversed-direction response is obtained by making the undercurrent receiverend relay 24 a polarized relay, as illustrated, so that it'will respond by dropping out and closing its back-contact 25, not only when the magnitude of the circulating current drops below a predetermined value, as in previous relay which' have been utilized in such pilot-wire supervisory circuits, but also the polarized relay 24 will respond by dropping out and closing its backcontact 25 when the direction of the circulating current is reversed, even though the magnitude is not reduced below its normal value.r The polarized relay v2li thus responds, by energizing an alarm-circuit, whenever there is an accidental reversal of the polarity of the pilot-wire Vconnections.

In Fig. 2, instead of relying upon the polarization of the undervoltage receiving-end relay 24 to obtain a selective action in the event of a reversal ofthe supervisory-current direction, we utilize an auxiliary rectier 26 in the supervisory direct-current circuit which is shunted across the terminals of the capacitor I4, said supervisory direct-current circuit including said auxiliary rectifier 26, the operating coil 21 of a combined overcurrent and undercurrent relay 28, and a resistor 29, although the relay 28 may be omitted, if it is not needed or desired, in any particular installation. The relay 28 has an undercurrent-responsive back-contact 3| which is utilized to energize an alarm-circuit as previously, and an overcurrent-responsive front-contact 32 which is .adapted to be closed only in response to an abnormally large circulating direct current, as will be subsequently described.

In the'system shown in Fig. 2, we have also shown means at the sending end for, at times,

predeterminedly increasing the magnitude of the circulating direct current in the pilot wire I2, such means being illustrated in the form of a resistor 33 and a shunting switch 34 for shunting some or all of th'e resistance 33, included in the direct-current output-circuit of the rectier il which supplies direct current to the terminals of the capacitor I3 at the sending end of the pilot-wire supervisory circuit. When the switch 35i is closed, either manually cr in respense to any automatic operation whatsoever, an intelligence-transmitting impulse is sent over the pilot wire I2 in the form of an increased magnitude of the supervisory direct current. This increase in magnitude need not, and preferably will not, be suflicient to cause the sendingend polarized relay IS to respond by closing its front-contact I9, but it will be suiiicient to cause the receiver-end relay 28 to respond by closing its overcurrent make-contact 32, thus energizing an intelligence-receiving circuit which may be utilized to respond, in any desired way, to the intelligence which was transmitted by the closure of the switch li at the sending end of the supervisory circuit.

purpose of transmitting an impulse or impulses which can be used for tripping, metering or re1aying of any kind, over the pilot wire, constitutes the subject-matter of the description and claims of a copendng application of M. A. Bostwick, Serial No. 346,319, filed July 19, 1940. The addition of the auxiliary rectifier 26 to such a circuit is one of the features of our present invention.

It should be noted that a relatively large resistance 22--23 (Fig. 1), or 26-214-29 (Fig. 2), should be included in the supervisory pilot-Wire circuit at the receiving end to aid in detecting high-resistance short-circuits which might oc cur on the pilot wire I2V close to said receiving end, that is, close to the end where the capacitor I3 is located, and opposite to the endV Where the direct-current source I6-I'I and the capacitor I3 are located.

In accordance with our invention, particularly in the form shown in Fig.'2where an intelligence-communicating lover currentV signal is transmitted over the supervisory-current channel of the pilot wire I2', a type of auxiliary rectier 26 should be utilized, having a considerable resistance to current-flow in the forward direction, as well as a very much higher resistance to current-flow in the reversed or backward or relatively non-conducting direction, so that the size of the resistor 29 may be reduced.

It is also extremely advantageous to choose a type of auxiliary rectifier 26 which automatically provides a considerable reduction in its forwardcurrent resistance when traversed by currents larger than the normal circulated supervisory current, thus materially reducing the eiective resistance of the' entire supervisory-current circuit when the switch 34 is closed for the purpose of increasing the magnitude Vof the supervisory current. This desired automatic change in the resistance of the supervisorycurrent circuit, in

from 2.3 millamperes to 4 milliamperes or even more, the effective resistance of the auxiliary rectler 26 will be smaller than for the normal circulating direct current.

In the event of an accidental reversal of the pilot-wire connections, our system which is shown in Fig. 2 will operate by giving an undervoltage alarm-circuit signal at both ends of the pilot Wire I2, as a result of the closure of both of the backcontacts 2% and 3l of the supervisory-circuit relays I8 and 28, respectively, said back-contacts 20 and 3l being closed because of the very great resistance of the rectifier 26 when an attempt is made to pass current in the wrong, or substantially non-conducting, direction therethrough. The provision for the energization of an alarmcircuit at the sending end as well as the receiving end of the supervised pilot-wire circuit is particularly advantageous in those systems where the receiving end of the supervised pilot wire is located in an unattended substation.

While we have illustrated and described our invention in two exemplary forms of embodiment, and while we have explained the essential principles of its operation as at present understood by us, we wish it to be understood that such illustration and explanation are intended by way of illustration and not altogether by Way of limitation, as it is obvious that many changes may be made by those skilled in the art without departing from the essential spirit of our invention. We desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

We claim as our invention:

l. In combination, a protected alternatingcurrent line-section, a pilot wire between the ends thereof, line-current-responsive means at each end of the pilot wire each deriving an altermating-currentl electrical quantity responsive to the line-current at its own end oi the line-section, electrical-connection means for utilizing the pilot wire to totalize the derived electrical quantities from the respective ends, line-ault-responsive relaying-means for responding to the totalized quantities, means, including a direct-current source at a rst end of the pilot wire, for circulating a direct current of a predetermined magnitude through said pilot wire, and means at the second end of the pilot wire for securing a selective action with respect to the circulating direct current according to the direction of said circulating direct current at said second end.

2. In combination, a protected alternatingcurrent line-section, a pilot wire between the ends thereof, line-current-responsive means at v each end of the pilot wire each deriving an alter- `tinctive ized undercurrent relay responsive to the circulating direct-current at the second end of the pielectrical-connection means for utilizing the pilot wire to totalize the derived electrica-l quantities from the respective ends, line-fault-responsive relaying-means for responding to the totalized quantities, means, including a direct-current source at a rst end of the pilot wire, for circulating a direct current or a predetermined nitude through said pilot wire, a rectifier serially included in the pilot wire at the second end thereof, and undercurrent direct-current relayingmeans for responding to the circulating direct current.

4.111 combination, a protected alternatingcurrent line-section, a piiot i 're between the ends thereof, line-current-responsive means at each end of the pilot wire each deriving an alternating-current electrical quantity responsive to the line-current at its own end ci the linesection, electrical-connection means for uti the pilot wire to totalize the derived electrical quantities from the respective ends, line-rauh',-

responsive relaying-means for responding to the totalized quantities, means, including a directncrmally continuously ciA rent of a predetermined mag pilot wire at all times when said v ,mt wire is intact, means for, at times, predeterminediy increasing the magnitude of the circuiating direct current in the pilot wire, a rectifier serialiy included in the pilot wire at the second1 end thereof, said rcctier having a lowered resistance at times of said predeterminedly increased direct-current new, undercurrent direct-Curie t rei-a infr-- means for responding to less than a predetermined magnitude of direct-current ow in the pilot wire, and overcurrent direct-current relaying-means for responding to said predeterminedly increased direct-current :dow in the pilot wire.

5. In combination, a pilot wire extending between two spaced points, means, including a direct-current source at a first end ci the pilot wire, for normally continuously circulating a direct current of a predetermined magnitude through said pilot wire at all times when said piot wire is intact, means at the second end of the piiot wire for securing a selective action h respect to the circulating direct current accor direction of said circulating direct en ent at said second end, means disposed at one point in the pilot wire for, at times, transmitting a disintelligence-communicating currentchange over the pilot wire, said distinctive intelligence-communicating current-che ge of such nature as not to actuate said directionrespcnsive means, and means selectiveiy responsive to said distinctive intelligence-coniinunicating current-change for providing a predetermined response at another point in the pilot wire.

6. In combination, a pilot wire extending between two spaced points, means, incl-ming a d.- rect-current source at a iirst end ci the piiot wire, for normally continuousiy circulating a direct current of a predetermined magnitude and direction through said pilot wire at all times when said pilot wire is intact, a polarized undercurrent relay responsive to the circulating direct current at the second end cf the pilot wire, means disposed at one point in the pilot wire for, at times, transmitting a distinctive intelligencecommunicating current-change over the pilot wire, said distinctive intelligence-conimunicating current-change being of such nature as not to actuate said direction-responsive means and means selectively responsive to said distinctive intelligence-communicating current-change for providing a predetermined response at another point in the pilot wire.

7. In combination, a pilot wire extending between two spaced points, means, including a direct-current source at a iirst end of the pilot Wire, for normally continuously circulating a direct current of a predetermined magnitude through said pilot wire at all times when said pilot wire is intact, a rectifier permanently serially included in the pilot wire at the second end thereof, undercurrent direct-current relaying-means for re'- sponding to the circulating direct current, means disposed at one point in the pilot wire for, at times, transmitting a distinctive intelligencecommunicating current-change over the pilot Wire, said distinctive intelligence-communicating current-change being of such nature as not to actuate said direction-responsive means, and means selectively responsive to said distinctive intelligence-communicating current-change for providing a predetermined response at another point in the pilot wire.

8. In combination, a pilot wire extending between two spaced points, means including a direct-current source at a rst end of the pilot Wire, for normally continuously circulating a dif rect current of a predetermined magnitude through said pilot Wire at all times when said pilot'wire is intact, means for, at times, predeterminedly increasing the magnitude of the circulating direct current in the pilot wire, a rectier serially included in the pilot wire at the second end thereof, said rectifier having a lowered resistance at times of said predeterminedly increased direct-current flow, undercurrent directcurrent relaying-means for responding to less than a predetermined magnitude of direct-current flow in the pilot Wire, and overcurrent direct` currentV relaying-means for responding to said predeterminedly increased direct-current iiow in the pilot Wire.

9. The invention as defined in claim 3, characterized by said undercurrent direct-current relaying-means being at the rst end of the pilot wire.

10. The invention as defined in claim 7, characterized by said undercurrent direct-current relaying-means being at the first end of the pilot Wire.

MYRON A. BOS'IWICK. ROY M. SMITH. 

